1. Field of the Invention
The present invention is directed to a multiple degree-of-freedom positioning device, and more particularly to such a positioning device having a manipulator shaft for manipulating an object to a desired position and orientation with a suitable compliance, such as used in an automated assembly line for mounting and assembling directionally oriented parts like many electronic components, or used to effect fine positioning of a machine table.
2. Description of the Prior Art
There have been proposed such a multiple degree-of-freedom fine positioning device as seen in U.S. Pat. No. 4,874,998, for controlling to move an object in multiple degree-of-freedom with suitable compliance. The patent discloses a hexagonal movable unit and a stator support unit for magnetically levitating the movable unit. The stator unit has a correspondingly shaped dual periphery within which the hexagonal movable unit is nested and carries six pairs of permanent magnets spaced circumferentially about the dual periphery in correspondence to six coils formed around the hexagonal movable unit. Each of the coils are disposed within a magnetic gap formed between the permanent magnets in each pair such that coil fields developed by energization of the respective coils interact with the related magnetic field at the gap to generate translational forces and rotational forces along and about three mutually perpendicular axes. An end effector is carried on the movable unit for effecting an intended work. However, the device of this patent is relatively bulky particularly in the radial direction of the movable unit because of the dual periphery structure of the stator unit and because of the circumferentially spaced magnets arranged about that dual periphery.
Another prior art multiple degree-of-freedom fine positioning device is disclosed in U.S. Pat. No. 4,602,848 which comprises a permanent magnet sleeve as a movable part of the device and two sets of stator coils arranged at the axial ends of the sleeve, respectively in parallel transverse planes. The stator coils are electrically energized to co-act with the external return field of the magnet sleeve to produce a reaction force acting on the magnet sleeve to move it in three mutually perpendicular axes including an axis of the magnet sleeve and to rotate it about two of the three axes excluding the axis of the magnet sleeve. In this patent, the stator coils are arranged radially outwardly of the magnet sleeve to thereby increase the radial dimension of the device. Therefore, this patent also fails to provide a compact structure particularly to the radial direction about a major axis defined by a movable unit or the magnet sleeve of the device.